Note: for the purposes of demonstration, three letter words have been substituted for real codons in this example. The real genetic code only uses four letters on the mRNA molecule; A, U, G, and C.

Changing one letter in the message changed one word, (codon), from DOG into DOT. Since each codon is translated into a single amino acid in the final polypeptide chain, changing one codon changed the type of amino acid that is placed in the polypeptide at this position.

The new polypeptide is different (has a different sequence of amino acids) than the original polypeptide. The effects of this change can vary from nothing to fatal depending on what role or function the protein plays in the cell or organism.